The invention relates to conveyor belts. More specifically, the invention is concerned with a plastic conveyor belt formed of interdigited modules serially connected by transverse connecting rods.
Plastic conveyor belts, made up of a series of interconnected modules, are well known. Often used in food handling and processing, the belts are frequently made of a temperature resistant and easily cleanable plastic. The modular construction, which often includes two or more modular sections side by side to make up the width of a belt, enables versatility in easily achieving many different belt configurations, lengths and widths. Some of the modular plastic conveyor belts are designed for a straight conveying surface only, with the return of the belt being underneath the active load bearing surface.
Other modularly constructed belts are designed for radius conveyor belt use. Use as a radius type conveyor belt involves considerations not present in a straight-flight belt. The belt must be guided around curves, and, as disclosed in U.S. Pat. No. 4,742,907, it is important that the belt modules not be guided around the curve by contact with surfaces at the inside of the curve. Such contact causes bunching and irregular travel of the belt at the inside of the curve. As discussed in the above mentioned patent, it is important to guide the conveyor belt around the outside of the curve for smooth travel, allowing the modules at the inside of the curve to collapse together.
A further consideration in radius type plastic conveyor belts is the high tension which is introduced into the belt on the outside of a curve. In U.S. Pat. No. 4,742,907 referenced above, outer sideplates are shown for insuring that the increased tension load can be handled at the outside of the curve in the belt.
The sideplates typically were attached at the ends of connecting rods used to interconnect plastic modules, with the rods extending continuously through the width of the belt. While effective for their intended purpose, these separate sideplates tended to place high shear loads on the typically plastic connecting rods while traversing the outside of a curve. They created a shear force acting on the rod, between the separate sideplate and the outside module. In addition, they required additional costs in parts and assembly time.
The plastic conveyor belt constructions described above typically had the connecting rods retained in place by "buttoning" or "rod heading" the ends of the rods after they were assembled in place. Thus, the plastic connecting rod, continuous throughout the width of the belt, was inserted transversely through the belt to interconnect the adjacent interdigited modules, then the ends of the rods were "buttoned" or "headed" by using a hot tool pushed against the rod end to partially melt and increase the size of the rod end. With both ends so treated, the rod was prevented from slipping out of the modules.
If sideplates were attached, as for a radius type belt, these would be inserted onto the ends of an adjacent pair of rods at the edge of the belt before buttoning the ends. The sideplates, such as shown in the above referenced patent, extended from one rod end to the next, so that a trailing end of one sideplate and a leading end of a successive sideplate would be present and overlapping at the end of each connecting rod. One end of each sideplate had a slotted hole for the connecting rod, to accommodate the shifting separation distance between successive belt modules as the belt entered the curve or exited a curve.
Because of the high shear loading on connecting rods at the outside of a curve, exacerbated by the separate sideplates, an expensive high-strength rod was required in most radius belts.
It is a principal purpose of the present invention to simplify modular plastic conveyor belt construction, particularly by eliminating the need for use of separate sideplates assembled onto the rods, by eliminating the need for "buttoning", and by an improved connecting rod construction. A related purpose is to eliminate shear acting between a separate sideplate and the outside module, present in prior constructions, by integrating the sideplate with projections of the outside module itself. These features make the belt and belt assembly more efficient in time and cost.